The invention relates generally to suspension locking of work vehicles. More particularly it relates to automatic suspension locking of skid steer vehicles when vehicle speed falls below a predetermined threshold.
Skid steer loaders are small highly maneuverable vehicles that are used in place of front end loaders, backhoes and the like in constricted environments. They are particularly useful due to their small size and maneuverability.
Their maneuverability is due to their method of steering. The wheels on one side of the vehicle (typically two) can be driven independently of the wheels on the other side of the vehicle. The wheels on each side of the vehicle can also be driven in opposite directions. The wheels themselves are not steerable. In other words, they cannot be turned about a generally vertical axis with respect to the chassis.
To steer a skid steer vehicle, the wheels on one side of the vehicle are driven at a different speed than the wheels on the other side of the vehicle. In an extreme case they are also driven in opposite directions. Thus, the wheels on one side can be driven forward as the wheels on the other side of the chassis are driven in reverse.
These different velocities (and/or different directions) cause the wheels to skid sideways as they rotate. As a result, one side of the vehicle advances faster than the other, and the vehicle turns. In the extreme case, when the wheels on either side are driven in opposite directions, the vehicle can rotate about a vertical axis within the perimeter of the vehicle""s chassis thereby giving it a turning radius of zero.
In addition to the maneuverability provided by the steering arrangement, skid steer vehicles also benefit from a narrow wheelbase and small width over wheels. A short wheelbase and small width over wheels permits the vehicle to be used in confined spaces, but prevents the use of sprung suspension.
The short wheel base, however, causes poor ride quality of the skid steer and limits the transportation roading speed. A skid steer vehicle tends to over bounce, roll, and pitch on rough terrain. A sprung suspension will improve the ride and the stability.
A sprung suspension used on a short wheelbase vehicle, however, would cause excessive diving as the implement connected to the loader arms is used to engage the ground. When the bucket or other implement mounted on the loader arms of the skid steer are pressed downward against the ground or are used to lift an object or a load of dirt (for example) the forces generated by engagement with the ground could cause a short wheelbase vehicle such as a skid steer loader to pitch up and down precipitously.
Another disadvantage of installing a sprung suspension on a skid steer is that the suspension makes the skid steer floating, which is good for high-speed roading, but not good for normal loader operations, such as digging, loading, and unloading, which require steady and firm platform.
For these reasons, skid steer vehicles having a short wheelbase (such as the common skid steer loader) have never been equipped with sprung suspensions.
What is needed, therefore is a suspension system for a skid steer loader that provides independent springing while the skid steer loader is being driven across a work site combined with some means for reducing or eliminating that springing when the skid steer loader is going slowly and the operator is manipulating the loader arms or operating the implement attached thereto.
It is an object of this invention to provide such a suspension system for a skid steer vehicle.
It is a further object of this invention to provide such a system that automatically engages and disengages the front end (and preferably rear end) suspensions in anticipation of the operator""s operation of the loader arms or implement (such as a bucket) attached thereto.
It is a further object of the invention to engage the front (and preferably rear) suspensions when the vehicle falls below a predetermined speed without requiring operator intervention thereby reducing the need for the operator to manipulate additional controls and thereby freeing the operator to concentrate on the manipulation of controls used to move the vehicle, the loader arms and the implement.
In accordance with a first embodiment of the invention, a skid steer is provided that includes a chassis having a left side and a right side; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; four control arms pivotally coupled to the chassis and coupled to the four wheels to permit the wheels to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; four hydraulic cylinders, each cylinder operably coupled to one of the wheels to control at least the vertical position of the wheels with respect to the chassis; a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground; and an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the four wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed.
The speed sensing means may be a wheel speed sensor, a hydraulic pump control circuit configured to generate a signal indicative of pump position, or a memory location in the electronic controller containing digital data indicative of the displacement of at least one of the first and second pumps. The digital data indicative of the displacement may be a value generated by the electronic controller. The vehicle may also include four valves, each of the four valves being coupled to one of the hydraulic cylinders to control an outflow of fluid from said one of the hydraulic cylinders. The electronic controller may be configured to automatically and repeatedly receive the signal indicative of the speed of the vehicle from the speed sensing means, to compare the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed, and to close the four valves when the vehicle is below the predetermined speed. The skid steer vehicle may include four gas-charged hydraulic accumulators, wherein each accumulator is fluidly coupled to and between one of the valves and that valve""s associated cylinder to block hydraulic fluid flow between the associated cylinder and said each accumulator.
In accordance with a second embodiment of the invention, a skid steer vehicle is provided a chassis having a left side and a right side; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation;
two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel to permit the associated forward wheel to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis; a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground; and an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the two forward wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed.
The speed sensing means may be a wheel speed sensor, a hydraulic pump control circuit configured to generate a signal indicative of pump position, or a memory location in the electronic controller containing digital data indicative of a commanded displacement of at least one of the first and second pumps. The digital data indicative of the commanded displacement may be a value generated by the electronic controller to control the displacement of at least one of the first and second pumps. The skid steer vehicle may include two valves, each of the two valves being coupled to one of the hydraulic cylinders to control an outflow of fluid from said one of the hydraulic cylinders. The electronic controller may be configured to automatically and repeatedly receive the signal indicative of the speed of the vehicle from the speed sensing means, to compare the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed, and to close the two valves when the vehicle is below the predetermined speed. The vehicle may include two gas-charged hydraulic accumulators, wherein each accumulator is fluidly coupled to and between one of the two valves and said one of the two valves associated cylinder to block hydraulic fluid flow from the associated cylinder to said each accumulator.
In accordance with a third embodiment of the invention, a method of controlling the suspensions of a skid steer vehicle is provided, the vehicle including a chassis having a left side and a right side, an engine coupled to the chassis, first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure, four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation, two control arms, each of the two control arms pivotally coupled to and between the chassis and an associated forward wheel to permit the associated forward wheel to pivot at least in a vertical direction with respect to the chassis, at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis, two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of said one of the two forward wheels with respect to the chassis, a speed sensing means to provide a signal indicative of the speed of the vehicle over the ground, and an electronic controller coupled to the speed sensing means and to the hydraulic cylinders that is configured to lock the two forward wheels in a vertical position with respect to the chassis when the vehicle falls below a predetermined speed, the method comprising the steps of reading the signal indicative of the speed of the vehicle; comparing the signal indicative of the speed of the vehicle with a value indicative of a predetermined speed; locking the two forward wheels of the four wheels to prevent vertical motion of the two wheels with respect to the chassis when the step of comparing indicates that the vehicle is traveling slower than the predetermined speed; and unlocking the two forward wheels to permit vertical motion of the two wheels with respect to the chassis when the step of comparing indicates that the vehicle is traveling above the predetermined speed.
The step of comparing may include the step of accessing an electronic memory location in the electronic controller that contains a value indicative of a commanded displacement of at least one of the first and second variable displacement pumps. The vehicle may also include two valves, wherein each of said two valves is fluidly coupled to an associated one of the two hydraulic cylinders to control the outflow of fluid from said associated one of the two hydraulic cylinders, and further wherein each of said two valves is operably coupled to the electronic controller to be controlled thereby. The step of locking the two forward wheels may include the step of closing the two valves. The step of locking the two forward wheels may include the step of blocking fluid flow from the two cylinders to two associated hydraulic accumulators.